This invention relates to a character reading system, and more particularly, to a preprocessing system for pattern recognition, and picture translation.
Generally, the percentage of error in the reading of a character reading system is influenced by the quality of the character pattern on a recording medium.
In mechanically printed or hand written characters, a portion of the character line becomes blurred or lost due to such causes as unsatisfactory type surface condition, non-uniform printing, non-uniform inking, inproper writing instruments, irregularity of the surface of the paper or the like. Even where the character lines are not blurred, when the contrast thereof with respect to the linear portions of the character is low due to a low percentage of the reflection of the paper, small contrast signals generated by a photoelectric converting circuit utilized to convert character patterns into electric signals will be lost by noises with the result that the character pattern will be detected as blurred patterns.
For the purpose of interpolating blurred or discontinuous character lines it has been proposed to compare contrast information of a point included in the pattern and that of nearby points for the purpose of judging whether a central point is on the character line or not depending upon whether the nearby point has a predetermined contrast difference from a predetermined threshold level or not. Such judgement means examination of the contrast of the character line. With this method however, non-uniform contrast of the character line will be judged as a blur or discontinuity of the character line or where a faint dirty spot is present on a portion other than the character, a contrast will be detected showing the dirty spot as a black spot. For this reason, with this method, it is necessary to use a proper expedient which prevents the faint dirty spot from being detected as a black spot whereas a character line having a low concentration is detected as a black line.
According to another method, the threshold level which is used to judge the contrast difference is made variable so that the threshold level is normally set to a definite level for effecting identification whereas when the character line is blurred, the threshold level is decreased but increased for character lines having higher concentration thereby effecting accurate identification.
The second method has a similar difficulty as in the first method. More particularly, where the threshold level is decreased for the purpose of judging character lines having a low contrast, even a faint dirty spot of the paper would be judged as a black spot whereas when the threshold level is increased the character line would be judged as discontinuous.
As disclosed in U.S. Pat. No. 3,688,266 we have proposed a character reading system capable of eliminating the defects described above wherein two types of patterns, that is a kernel pattern P having a high threshold level and a reference pattern Q having a low threshold level are used for the purpose of positively detecting only the characters but not detecting faint dirty spots other than the characters.
As shown in FIG. 1, according to this system, a character 2 on a recording medium 1 is scanned by a scanning device 4 through an optical system 3, and the contrast signals at various cross points of column lines and row lines which cover the character pattern are passed through a first threshold circuit 5 having a high threshold level A for discriminating two values of white and black, and a second threshold circuit 6 having a low threshold level for discriminating two levels of white and black and a kernel pattern P obtained by the first threshold circuit 5 and a reference pattern Q obtained by the threshold circuit 6 are temporarily stored in two dimensional registers 7 and 8 respectively. Then, in a pattern processing circuit 9, continuous character lines are obtained from patterns P and Q by interpolating the discontinuous portions of the character lines of the pattern P with the pattern Q thereby forming a character pattern R from which black spots caused by dirty spots other than the character lines have been eliminated. The character pattern R is then stored in a two dimensional register 10 as a normal character reading pattern.
According to this system, since the character pattern R is formed by extracting only the character portion, it is possible to obtain a character reading system which can operate stably and permits relatively high allowance for the quality of printing. In other words, this system can accurately read characters of poor printing quality.
However, this system still involves a number of problems to be solved. One problem is that the circuit wiring for performing the connecting operation is extremely complicated and the second problem is that the time required for the connecting operation is long.
These problems will be described briefly in the following.
The two dimensional registers 7 and 8 and the pattern processing circuit 9 shown in FIG. 1 were constructed as shown in FIG. 2. In FIG. 2, (20-1).about.(20-9) represent memory elements (flip-flop circuits, for example) for storing the white and black states of the picture elements of the pattern P whereas (20-10).about.(20-18) represent the memory elements for storing the white and black states of the picture elements of the pattern Q. Although in FIG. 2, only 9 memory elements are shown for storing patterns P and Q respectively, actually, these memory elements are arranged in a matrix of M.times.N (for example, 128.times.128). Information of the memory elements P(x,y) and Q(x,y) corresponding to a position (x,y) of the two dimensional registers 7 and 8 determines the white and black states of a memory element R(x,y). Considering a case of determining the white and black states of the memory element R(x,y) with reference to FIG. 2, the memory element R(x,y) is determined by the output of an AND gate circuit 22 which is supplied with the output of the memory element Q(x,y) and the output of an OR gate circuit 23. The OR gate circuit 23 is supplied with the output signals of the memory units P(x,y), R(x+1, y), R(x, y-1), R(x-1, y) and R(x, y+1). Accordingly, where the content of the memory element Q(x,y) is "1" (that is black) when the character is detected with the low threshold level, and at content of P(x,y) and the contents that is the contents of R(x+1, y), R(x, y-1), R(x-1, y) and R(x, y+1) of four points surrounding R(x,y) are "1" (that is black) where the character is detected with the high threshold level, the memory element R(x,y) is determined as "1" (that is black). Such judgement is made throughout the pattern and the resulting pattern R is stored in a two-dimension register (register 10 shown in FIG. 1) having M.times.N bits (for example, 128.times.128).
As can be noted from the foregoing description since the circuits (AND gate circuit 22 and the OR gate circuit 23) for effecting the connecting operation are provided throughout the pattern between M.times.N memory elements adapted to store the pattern P and M.times.N memory elements adapted to store the pattern Q, the wiring of the connecting operation circuit is extremely complicated and bulky, thus increasing the size of the apparatus.
In the prior art processing system shown in FIGS. 1 and 2, the result of processing which is performed throughout the pattern by using the complicated connecting operation circuit described above is once stored in M.times.N memory elements provided for storing the pattern R, and after the connecting operation of the entire pattern has been completed the contents of the M.times.N memory elements which store the pattern R are sequentially read out. As can be noted from FIG. 2, the connecting operation of one point (x,y) influences all other points, so that connecting operation of that point (x,y) is completed only when the connecting operations throughout the pattern have been completed. For this reason, until the connecting operation of the entire pattern has been completed, it is impossible to derive out the contents of the memory elements which are storing the pattern R with the result that it was impossible to improve the processing speed of the character reading apparatus. Especially, where the longitudinal dimension of the pattern is large, the connecting operation requires a long time, so that where the patterns continue infinitely in the longitudinal direction, the connecting operation would never terminate. For this reason it has been desired to provide a more efficient connecting operation system than that shown in FIGS. 1 and 2.